Improved flexural strength has been required for a frame body used particularly for a center pillar of a vehicle body of a vehicle in view of side impact performance of the vehicle. To improve the flexural strength, for example, Patent Document 1 teaches a center pillar including an outer panel positioned outside the vehicle body, an inner panel positioned inside the vehicle body to form a closed cross-section with the outer panel, and a reinforcement arranged between the outer panel and the inner panel.
Patent Document 2 teaches that an outer wall positioned outside the vehicle body is made thicker than a front wall and a rear wall, and a thickness increasing part which is gradually increasing in thickness toward the outside of the vehicle body from a substantial center of the vehicle in a width direction of the vehicle is formed inside the front wall and the rear wall.
Patent Document 3 teaches a vehicle body part which is made of a steel plate, and is substantially in the shape of a rectangular tube with rounded edges, and at least one of the edges and the vicinity thereof is hardened.